Electronic device, method for using electronic device, and electronic device system for reserving bus usage time on a bus to conduct communications between electronic devices

ABSTRACT

An IRD  103  supplies broadcasting data on a bus a desired time period. When the IRD  103  performs a reservation of the bus usage, the IRD  103  request current bus usage information and information of the bus reservation from all devices connected by the bus, such as a DVD  104 , a D-VTR  101 , a D-VTR  102 , a CAM  105 , a TV  100 , and a isochronous manager  107  of the D-VTR  101 . The isochronous manager  107  and each device answer by sending the bus usage information to the IRD  103  and reservation information. The IRD  103  judges a possibility of the reservation from the answer information. If the reservation is possible, it performs the reservation operation. IF the reservation is impossible, then the reason is displayed on a TV  100 . Therefore, it is possible to prevent a usage of a device that excesses the bus transferring capacity.

TECHNICAL FIELD

This invention relates to a technique for controlling communication inan electronic device system, including devices, such as an Audio Visualdevice (hereinafter, “AV device”) that deals with visual information andaudio information, and an information processing device, connected by acommunication bus. Especially, the technique operates to prevent a useof the electronic device system that exceeds data the transfer capacityof the communication bus.

BACKGROUND ART

The IEEE 1394 serial bus is thought of as a network system that enablesa transmission of data by isochronous communication and a transmissionof a control signal by asynchronous communication between an AV deviceand an information processing device. The IEEE 1394 serial bus isstandardized to “IEEE STD 1394-1995” as “IEEE STANDARD FOR A HIGHPERFORMANCE SERIAL BUS.” As an example of using IEEE 1394 serial buses,Japanese published unexamined patent application No. H08-47058 describesthat “a method for selecting input devices” that can display only theidentification of a device that is able to output an information signal,as an input available device in a system that is connected to aplurality of electronic devices by way of a communication bus.

Further, an “AV/C Digital Interface Command Set”, which includes controlsignals to control an AV device for playback and recording of AV data byusing a 1394 IEEE serial bus, has been opened to the public by the “1394Trade Association.” However, in the standard technique for the IEEE 1394serial bus, in case a plurality of electronic devices performisochronous communication simultaneously, the available band width andnumber of channels of the bus are exceeded, and so some of theelectronic devices that try to perform communication can not use the busbecause of the short available band width and limited number of channelsof the bus.

Consider a case wherein, in a network, for example, in which a digitalreceiver IRD (hereinafter “IRD”) is connected to a device such as adigital videotape recorder D-VTR (hereinafter “D-VTR”), a reservedrecording is performed by the network. When the other electronic devicesthat are connected in the network use the bus during the reservedrecording time, and the bus width that the IRD wants to use is largerthan the available bus width at that time, the IRD cannot secure thenecessary bus width. As a result, the reserved recording can not beperformed because data can not be satisfactorily transmitted from theIRD to the D-VTR.

Further, in the input device selection method and AV/C Digital InterfaceCommand Set, a method of selecting the input device at the present time,and a method of transmitting the data and the control signals at thepresent time are only considered.

SUMMARY OF THE INVENTION

The main object of the present invention is to solve the foregoingproblems. In the case of an electronic device system in which an AVdevice and an information processing device are connected by acommunication bus, and a reserved playback time and a reserved picturerecording time are established, an inquiry is made of the connecteddevices to obtain information about each reservation. Then, on the basisof answer information received from the devices, it is determined how toperform a reservation for a communication resource, so that a usage thatexceeds the transfer capacity of the communication bus is prevented,thereby allowing the reservation by the communication resource to beaccepted.

Further, in accordance with this invention, in case a reservation or animmediate communication is impossible, the reason for this can bedisplayed. In addition, in case usage of a bus is prohibited becauseother devices have reserved the bus, the reason for this can bedisplayed.

This invention relates in particular to a system in which a device, suchas AV device, is connected to an information processing device by a bus.In order to communicate in a reliable manner on the bus, a device thatcan perform data reproduction in the system inquires of the connecteddevices for reservation information. Responsive to an answer from theconnected devices, the device has an element that can judge theavailability of the bus transferring capacity not so as not to exceedthe capacity of the bus. Therefore, a device that wants to use the buscan perform an information transfer. Further, by judging whether theabove-mentioned usage of the bus is available, in a case where it isimpossible to use the bus, the device has an element that communicatesthe reason to a video display device. Therefore, the device can performan appropriate setting for the reservation to avoid problems in the useof the bus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an electronic device systemaccording to a preferred embodiment of the invention.

FIG. 2 is a block diagram illustrating the electronic device structure(IRD) according to the preferred embodiment of the invention.

FIGS. 3(a) and 3(b) are diagrams illustrating examples for securing abus reservation according to the preferred embodiment of the invention.

FIGS. 4(a) and 4(c) are diagrams is a drawing illustrating an examplefor securing immediate communication according to the preferredembodiment of the invention.

FIG. 5 is a flow chart illustrating a reservation process according tothe preferred embodiment of the invention.

FIG. 6 is a diagram illustrating an example of a transmission datastructure according to the preferred embodiment of the invention.

FIG. 7 is a diagram illustrating an example of a response data structureaccording to the preferred embodiment of the invention.

FIG. 8 is a diagram illustrating an example of a stored reservation datastructure according to the preferred embodiment of the invention.

FIG. 9 is a diagram illustrating an example of a stored immediatecommunication data structure according to the preferred embodiment ofthe invention.

FIG. 10 is a diagram illustrating an example of a bus information datastructure according to the preferred embodiment of the invention.

FIG. 11 is a diagram illustrating an example of a bus reservationdisplay according to the preferred embodiment of the invention.

FIG. 12 is a diagram illustrating an example of a bus unavailablereservation display according to the preferred embodiment of theinvention.

FIG. 13 is a flow chart illustrating an immediate communication processaccording to the preferred embodiment of the invention.

FIG. 14 is a diagram illustrating an example of an immediatecommunication display according to the preferred embodiment of theinvention.

FIG. 15 is a diagram illustrating an example of a bus unavailableimmediate communication display according to the preferred embodiment ofthe invention.

FIG. 16 is a flow chart illustrating a response process according to thepreferred embodiment of the invention.

FIG. 17 is a block diagram illustrating an example of a system includingdegree of priority processing according to the preferred embodiment ofthe invention.

FIG. 18 is a diagram illustrating an example of a degree of priorityprocessing of a CAM according to the preferred embodiment of theinvention.

FIG. 19 is a diagram illustrating an example of a display of degree ofpriority processing of a DVD according to the preferred embodiment ofthe invention.

FIG. 20 is a diagram illustrating an example of a reservation operatingdisplay by a personal computer according to the preferred embodiment ofthe invention.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

With reference to the drawings, a preferred embodiment of the presentinvention will be explained. In the preferred embodiment of the presentinvention, especially, one that involves a system of electronic devices,such as an AV device and an information processing device, that areconnected by a bus, which is available for isochronous communication,like an IEEE 1394 bus, it is possible to effect a bus usage reservationand to effect immediate isochronous communication in a trouble freemanner.

The isochronous communication on a IEEE 1394 serial bus is performedapproximately every 8 KHz (KILOHERTZ). That is a secured datatransmission mode of a transmission band. The data transfer is performedby packet transmission, and the packet data consists of a header partand a data part, wherein the header part stores information, such as achannel number and a transmission data size, and the data part storestransmission data in units of 4 bytes. Further, in IEEE 1394, there isan asynchronous data transmission mode that is called asynchronouscommunication. The asynchronous communication mode is mainly used fortransmission of a command.

FIG. 1 is a block diagram illustrating a network system according to apreferred embodiment of the invention. A TV 100 in the form of atelevision receiver, a D-VTR 101 and a D-VTR 102 which perform recordingand reproducing of AV data, an IRD 103 which is a digital satellitebroadcasting receiver, a digital video disk unit DVD 104 (hereinafter“DVD”) which performs reproducing of AV data, a digital video camera CAM105 (hereinafter “CAM”) which performs recording and reproducing of AVdata, and a personal computer PC 106 (hereinafter “PC”) are connected byan IEEE 1394 bus cable 108. In the case of isochronous communication onthe IEEE 1394 bus, one of the devices connected by the bus is used as anisochronous manager 107 so as to manage the bus width and channels. Inthis embodiment, the D-VTR 101 is provided with the isochronous manager107, however, another device, such as the DVD 104, could be providedwith the isochronous manager function.

As disclosed in FIG. 1, the configuration of the device connection canbe a daisy chain connection or a tree connection or various combinationsthereof Although it is not shown in FIG. 1, there is a case in whichdevices, such as a hard disk device, a printer, a scanner and an audiodevice, also are connected in the system.

FIG. 2 is a block diagram illustrating the internal structure of the IRD103, which is one of the electronic devices in the system, according tothis preferred embodiment of the invention. The numeral 200 designatesan internal bus of the IRD. The numeral 201 designates an input unit bywhich reservation setting data is input. The numeral 202 designates adisplay unit for displaying required data relating to the reservationsetting data. The numeral 203 designates a CPU that performs overallcontrol and processing of the bus reservation of the IRD. The numeral204 denotes a memory for storing reservation data, and for performingother memory functions. The numeral 205 designates a communication unitfor communicating with other devices. The numeral 206 designates a timeof day control unit for managing the time. The numeral 207 denotes atuner for receiving a broadcast wave. The numeral 208 denotes a pictureprocessing unit for decrypting received picture data, and so on. Thenumeral 209 designates a working memory for storage of working data whenthe CPU performs various processes. The display 202 may be located notonly on the body of the IRD, but also on a remote controller, or the TV100 may be utilized for this function.

The following cases represent ways in which a communication on the buscan be established.

(1) A case in which the bus transmission capacity (hereinafter “buswidth”) of a time zone in the future is secured for a bus reservation toeffect a further communication.

(2) A case in which the bus width from the present time is securedimmediately for an immediate communication for the duration of thecommunication. While the case (1) provides bus width security for anappointed time zone, the case (2) can be thought of as providing buswidth security, without an appointed time zone, from the present time.

For example, in case the TRD 103 wants to secure a particular bus widthfor a time zone in the future, as shown in FIG. 3(a) and FIG. 3(b), thefollowing situations may be considered in the case (1).

(a) A situation in which there is an available bus width relative to theoverall bus width in the time zone that is to be secured forreservation, as seen at 300 in FIG. 3(a).

(b) A situation in which there is not sufficient bus width availablerelative to the overall bus width in the time zone that is to be securedfor reservation, as seen at 301 in FIG. 3(b).

On the other hand, in case the IRD 103 wants to secure a certain buswidth to perform immediate communication, as shown in FIGS. 4(a), 4(b)and 4(c), the following situations may be considered in the case (2).

(c) A situation in which there is an available bus width for the presenttime and for a time in the future relative to the overall bus width ofthe time period that is to be secured immediately, as indicated at 400in FIG. 4(a).

(d) A situation in which there is an available bus width for the presenttime, but no margin for a time in the future relative to the bus widthof the time period that is to be secured immediately, as indicated at401 in FIG. 4(b).

(e) A situation in which there is not sufficient bus width with at leasta margin for the present time relative to the overall bus width of thetime period that is to be secured immediately, as indicated at 402 inFIG. 4(c).

The process to secure a reservation for a communication resource for atime in the future in the case (1), will be explained with reference tothe flowchart of FIG. 5, the packet structure of FIG. 6 and FIG. 7, andthe storage data format of FIG. 8, FIG. 9 and FIG. 10.

First there will be an explanation of the process carried out in thecase of FIG. 3(a). In FIG. 5, in step 500, the reservation program iscalled at the time of starting a reservation operation. The starting ofthe reservation operation involves execution of the reservationprocessing program stored in the ROM 210 after the CPU 203 sensesactuation of a reservation starting button via the input unit 201. Instep 501, the CPU 203 inquires into the bus usage and the busreservation situation. The IRD 103 responds to the inquiry by sending arequest for immediate communication information and reservationinformation to the isochronous manager 107 and the devices connected tothe bus. At that time, as shown in FIG. 6, a packet is produced thatconsists of a function code representing the substance of the request,and the packet is transmitted to each device connected to the busthrough the communication unit 205 as a request for information.

In step 502, an answer, including data representing the immediatecommunication information and the reservation information for the bus,information which represents bus usage information, is received. Theanswer is received by the communication unit 205, and the received dataare stored in the working memory 209. For example, the communicationunit 205 receives data indicating a current available bus width 1000 andchannel information 1001 from the isochronous manager 107, as shown inFIG. 10, as well as answer data in the form of immediate communicationinformation and reservation information from the connected devices, asshown at 702 of FIG. 7. In this case, for example, it will be assumedthat the content of the answer data received from the isochronousmanager 107 indicates that 80 MBPS of the bus is available at present.Further, it will be assumed that the answer content from the D-VTR 101indicates that 30 MBPS of the bus width is reserved from 18:00 to 20:00on December 14.

In step 503, a user inputs usage information indicating a desired use ofthe bus (hereinafter “reservation-desired data”) relating to the bususage, such as a desired time period for reservation of the bus. Thedata is inputted via the input unit 201 and is stored in the workingmemory 209. For example, as shown at 1101 of FIG. 11, the user inputsreservation-desired data, such as a bus width of 20 MBPS (MEGA BIT PERSECOND), for a period from 19:00 to 21:00 on December 14 to the IRD103.

In step 504, it is determined whether the reservation is possible. Thereservation-desired data stored in the working memory unit 209, thereceived immediate communication information, and the receivedreservation information are compared. The CPU 203 performs the judgementusing a scan process of examining whether the requested time period thatis to be reserved is already reserved. It is also possible to subtractthe bus width designated in the reservation request from the maximum buswidth that is available in the requested time period and to perform therequired judgment to determine if the reservation is possible bywell-known processing. As seen in FIG. 3(a), the time period for whichthe D-VTR 101 is reserving the bus is within the time period that theIRD 103 wants to reserve the bus for the period from 19:00 to 20:00.But, even if 20 MBPS of bus width secured in the immediate communicationis considered, the overall bus width that is available for the timeperiod in which the reservation overlaps the other usage is 50 MBPS.Therefore, it is determined that the bus width of 20 MBPS that the IRD103 wants to reserve can be reserved, and so the process advances tostep 505.

In step 505, the reservation-desired data is stored as bus usageinformation, and then the process advances to step 506. The reservationusage information is stored to the memory 204. FIG. 8 shows an exampleof the stored data structure. A reservation time zone field 800 storesinformation indicating the reservation time period of the reserveddevice. A reservation bus width field 801 stores information indicatingthe reserved bus width. A reservation channel number field 802 storesinformation identifying the reserved channel number. In step 506, thereservation process is ended.

The following is an explanation of the process carried out in the caseof FIG. 3(b). The situation is the same as that of the above-mentionedcase (1), except for the availability of bus width.

In step 503, a user inputs the reservation-desired data, such as adesired time period for reservation of the bus. The data is inputted viathe input unit 201 and is stored in the working memory 209. However, inthis case, if the IRD 103 makes a reservation that is more than 70 MBPS(MEGA BIT PER SECOND) for the time period from 19:00 to 21:00 onDecember 14, the bus width that is available for that time period willbe insufficient. In step 504, therefore, when the possibility ofreservation of the time period is considered, it is determined that thereservation is impossible, and so the process will advance to step 507.In step 507, the reason why the reservation is not possible isdisplayed, as seen at 1201 in FIG. 12, and the process advances to step508.

In step 508, it determines whether the request for a reservation is tobe retried or ended. For example, a character line requesting whetherthe reservation is to be retired or ended is displayed on the displayunit 202, and then the user inputs a selection via the input unit 201.The inputted selection information is judged by the CPU 203 to determinewhether the process is to advance to step 503 or to step 506. Asmentioned above, the device that seeks to obtain the reservationrequests reservation information from the devices connected to the bus.Then, a determination as to the possibility of obtaining the reservationis performed based upon the answer information received from otherdevices and the information received from the bus manager. Even in acase where a reservation cannot be granted because there already isanother reservation for the same time period reserved by other devices,a reservation may be canceled by judging the priority of each user inthe IRD 103 and granting a reservation to the user having a higherpriority.

Next, the process to secure a reservation for a communication resourcefrom the present time to effect an immediate communication in the case(2) will be explained with reference to the flowchart of FIG. 13, thepacket structure of FIG. 6 and FIG. 7, and the storage data format ofFIG. 8, FIG. 9 and FIG. 10.

The following is an explanation of the process carried out in the caseof FIG. 4(a).

Step 1300 is performed at the time of the start of immediatecommunication operation. The starting of the immediate communicationoperation involves execution of an immediate communication processingprogram stored in the ROM 210 after the CPU 203 senses actuation of animmediate communication starting button via the input unit 201. In step1301, the IRD 103 responds to an inquiry from the CPU 203 by sending arequest for immediate communication information and reservationinformation to the isochronous manager 107 and the devices connected tothe bus. Then, as shown in FIG. 6, a packet is produced that consists ofa function code which is transmitted to each device connected to the busthrough the communication unit 205.

In step 1302, an answer including data representing the immediatecommunication information and the reservation information is received inthe communication unit 205, and this data is stored in the workingmemory unit 209. For example, the communication unit 205 receives dataindicating a current available bus width 1000 and channel information1001 from the isochronous manager 107, as shown in FIG. 10, as well asanswer data in the form of immediate communication information andreservation information from the connected devices. In this case, forexample, it will be supposed that the content of the answer data fromthe isochronous manager 107 that 80 MBPS of the bus is available atpresent. Further, it will be supposed that the answer content from theD-VTR 101 indicates that 30 MBPS of the bus width is reserved from 18:00to 20:00 on December 14. In addition to that, it is supposed that theanswer from the D-VTR 104 indicates that 20 MBPS of the bus width is tobe used for the immediate communication.

In step 1303, the bus width that is necessary for the communication ofdata, that is, desired bus usage information, is inputted and is storedin working RAM 209. For example, as shown at 1401 in FIG. 14, adesignation of 20 MBPS is stored as the bus width that is necessary forthe immediate communication.

In step 1304, it is determined whether the immediate communication ispossible. The answer data and the immediate communication data arecompared. The CPU 203 performs the judgement using a scan process ofexamining whether the requested time period that is to be reserved hasalready been reserved. It is also possible to subtract the bus widthdesignated in the reservation request from the maximum bus width that isavailable in the requested time period and to perform the requiredjudgment to determined if the reservation is possible by well-knownprocessing. The available bus width that can be used at present is 80MBPS, and the D-VTR has reserved use in the interval from 19:00 to 20:00in the time zone in the future. Since the available bus width in thetime period remains 50 MBPS, if the secured 20 MBPS for the immediatecommunication is subtracted from the available bus width, it can be seenthat the 20 MBPS bus width for the immediate communication of the IRD103 is available, and so the process advances to step 1305.

In step 1305, the immediate communication information is stored in thememory 204, and then the process advances to step 1306. FIG. 9 shows anexample of the stored data structure. An immediate communication buswidth field 900 carries information concerning the usage bus width. Animmediate communication channel field 901 carries information as to thereserved reserving channel number. In step 1306, the immediatecommunication process is ended. At this point, execution of theimmediate communication processing program, which was called from theROM 210, is finished.

The following is an explanation of the process carried out in the caseof FIG. 4(b). The situation is the same as that of the above-mentionedcase (2), except for the availability of bus width.

In step 1303, for example, a designation of 60 MBPS as the bus widththat is necessary for immediate communication is stored in the workingRAM 209. In this case, in step 1304, because the bus width isinsufficient in the reserved time period of the D-VTR 101, it is judgedthat the bus width necessary for the immediate communication cannot besecured, and the process advances to step 1307. In step 1307, the reasonwhy the immediate communication cannot be allowed is displayed, as seenat 1501 in FIG. 15, and the process advances to step 1308. In step 1308,it is determined whether the request for the immediate communication isto be retried again or ended. In case of the case of FIG. 4(b) , if theimmediate communication is changed so as to require communication onlyuntil the starting time of the D-VTR 101, it can be secured until 19:00.

The following is an explanation of the process carried out in the caseof FIG. 4(c). The situation is the same as that of the above-mentionedcase of FIG. 4(b) in that it also involves an insufficiency of buswidth.

In step 1303, it will be assumed that a designation of bus width that islarger than 90 MBPS, representing the bus width that is necessary forthe immediate communication, is stored in the working RAM 209. In thiscase, in step 1304, it is determined that the necessary bus width forthe immediate communication is not available because the bus width isalready insufficient at present, and so the process advances to step1307. In step 1307, the reason why immediate communication cannot beallowed is displayed, and the process advances to step 1308. In step1308, it is determined whether the request for immediate communicationis to be retried again or ended.

As mentioned above, the device that tries to obtain a reservation foruse of the bus requests immediate communication information andreservation information from the devices connected to the bus. Then, thejudgment as to the possibility of obtaining a reservation is performedbased upon the answer information received from the other devices andthe information received from the bus manager. Even in a case where theimmediate communication cannot be allowed because of another reservationin the same time period, which is reserved by other devices, areservation may be canceled by judging the priority of each user in theIRD 103 and canceling in a reservation having a lower priority, therebymaking immediate communication possible.

In this embodiment, the possibility of obtaining a reservation isdetermined in step 504, however, a restriction of the band width andchannel number can be effected so as to allow immediate communication ina reserved time period easily. For example, if the band width andchannel are set such that only 80% of the maximum value of each buswidth and channel number are possible to make the reservation using areservation processing program stored in the ROM 210, at least 20% ofthe maximum value of each bus width and channel number will be availablefor an immediate communication, even in a reserved time period.

Further, the system can display the tackling method that is reserved inwhich reservation of which device is canceled in the cases that it isn'tpossible to reserve the bus. Then, to secure the needed bus width whenthe bus width runs short, a calculation is made as to which reservationof other devices has to be canceled by the CPU 203 in the reservationprocessing of step 504, and the result is displayed on display unit 202so that a reservation on reservations selected by the user may becanceled.

In the above-mentioned embodiment, all devices reply to a demand for bususage information, but this can be performed with only the reservationdevice which is going to communicate in the future or communicateimmediately.

In FIG. 16, the example of a procedure for processing the information inthe device that responds at this time is shown. In this figure, a casein which other electronic devices have transmitted the immediatecommunication information of the bus and an answer requirement packet ofreservation information to IRD 103 will be explained.

In step 1600, the process starts when the answer requirement packet isreceived. It is judged whether the communication unit 205 receives thepacket including the function code of the answer requirement issued bythe CPU 203, and, if the packet has been received, execution of ananswer processing program stored in ROM 210 is started. In step 1601,the function code is decoded. The CPU 203 refers to the function codetable in ROM 210 for this purpose, and the function code is interpreted.In step 1602, in case the function code is an answer requirementconcerning a current usage or the present of a reservation, the processadvances to step 1603. In case it is another function code, the processadvances to step 1606.

In step 1603, the answer processing is performed. The CPU 203 refers tothe memory 204 in order to examine whether the bus is reserved or isbeing used for immediate communication by its own device. If there isreservation information and immediate communication information, thatinformation is expanded to the working RAM 210 and is adjusted to ananswer format. If there is no reservation information and immediatecommunication information, the process advances to step 1605. In step1604, an answer packet is transmitted. The answer packet adjusted to theanswer format is transmitted from the communication unit 205. Theprogram is ended in step 1605. The answer-processing program in the ROM210 is ended. In step 1606, the CPU 203 performs the processing thatcorresponds to the function code, and the process advances to step 1605.

By this procedure, only the devices that have established a reservationor are involved in immediate communication can respond. Further, forexample, IRD 103 sends information identifying the time period that isto be reserved to each device, but only those devices that have areservation during the same time period or that are using the bus atpresent can respond. In this case, the information identifying the timeperiod that IRD 103 wants to reserve is added to the function code 701.Further, for example, in the reservation answer processing program ofthe D-VTR 101, in step 1304, the D-VTR 101 judges if there is areservation during the desired time period or there is a usage of thebus at present, and it may determine as a result whether it will send asanswer packet.

Further, a priority of the bus usage and the granting of reservationscan be set up. This will be explained with reference to FIG. 17, FIG. 18and FIG. 19 for a case in which it is desired to sent video informationfrom a DVD1704 to a PC 1706 and also to perform a dubbing activity in aD-VTR 1702 from a CAM 1705. At this time, it is assumed that urgentinformation has been received from a broadcasting radio wave or anetwork through the IRD1703 and the PC 1706, and that this urgentinformation is to be displayed on a TV 1700. When there is aninsufficient margin in the bus width, there is a possibility of notbeing able to display the urgent information. At this time, as seen at1801 of FIG. 18, the priority of the bus usage for a video recordingfrom the CAM 1705 to the D-VTR 1702 is set as “priority”. Further, thepriority of the bus usage for a soft playback from the DVD1704 to the PC1706 is set as “normal”, as seen at 1901 in FIG. 19. Further, thepriority of the bus usage for the transmission of urgent informationfrom the IRD1703 to the TV 1700 is set as “most priority”. In this case,even in the case where there is sufficient available bus width, the bususage for the soft playback from the DVD 1704 to the PC 706, thepriority of which is “normal”, is stopped, and so the bus width that isnecessary for transmission of the urgent information can be secured andthe information can be displayed on the TV 1700. In case a PC1706 with afunction that can control other devices is connected in the system,while a normal reservation operation is performed by each device, thereservation operation also can be performed by the PC1706 collectively.In FIG. 20, an example of the screen produced by the personal computeris shown. The screen 2000 is produced on a personal computer monitor. Abus resource that has secured a reservation time and date for use of thebus is displayed on a display window 2002. In the display window, theoperation screen is displayed. Then, the reservation of a program and atime is set. The operation window of the D-VTR is displayed on a displaywindow 2003. A mode of the video is set.

Further, it is assumed that a device is plugged or unplugged in the IEEE1394 network and that a bus reset has occurred in FIG. 5. In this case,if the IRD 103 has a reservation to record a video program with theD-VTR 101 from the IRD 103, the IRD is unplugged from the network, as awhole, so that the possibility of sufficient reservation bus width inthe network increases. A device that is using the bus or obtains areservation calls step 500 and in step 501, it requests information fromeach of the devices that are connected to the bus again. Because eachdevice stores its usage or reservation information in the memory 204,each device automatically transfers the information in step 503, and thecurrent usage or reservation status of the bus is judged in step 504. Ifa problem does not arise, the process can return to a state whichexisted before the bus reset occurred. However, in case of not beingable to return for some reason, in step 507, the reason why the processis not able to return is displayed.

Further, in the above-identified embodiment, in step 507, a warningscreen is displayed as a means for displaying the reason why areservation is impossible. However, the warning screen can be displayedon not only the TV monitor, but also on a liquid crystal screen of aremote-controller or an operation panel of a electronic device or adisplay apparatus. Instead of the warning screen, a warning sound, anaudio message, or music may be outputted to an audio output device. Inaddition to that, a means that a user can visually recognize, such as awarning using a blinking light emitting diode, can be employed.

As mentioned above, since this invention is able to prevent areservation that will exceed the bus transferring capacity, a reliablecommunication, such as at the time of recording, can be performed.Further, in case the reservation of the bus is impossible, the user cantake steps to adjust the conditions to allow communication because thereason why the reservation is impossible is displayed.

Further, there is a case wherein, when a device attempts to start animmediate communication after having secured the bus, the device may notbe able to complete the communication on the bus as a result of areservation of the bus by another device in the future. In the case of adevice that desires to effect an immediate communication or reserve acommunication time, but can not perform the communication because of bususage, this invention gives a warning to the user by displayinginformation giving the reason for the problem.

What is claimed is:
 1. In a system including a plurality of electronicdevices connected to each other by a bus, wherein each electronic deviceis capable of transmitting or receiving information to and from anyother electronic device via said bus, each electronic device comprising:transmitting means for transmitting a request for bus usage includingbus usage desired information to said any other electronic device viasaid bus; and transmitting means for transmitting bus usage informationanswering said request for bus usage from said any other electronicdevice via said bus in response to the transmitted request for said bususage from said any other electronic device via said bus, wherein saidbus usage desired information and said bus usage information includes atleast a bus transferring capacity, a starting time of bus usage, and afinishing time of bus usage information.
 2. In a system including aplurality of electronic devices connected to each other by a bus,wherein each electronic device is capable of transmitting or receivinginformation to and from any other electronic device via said bus, eachelectronic device comprising: transmitting means for transmitting arequest for bus usage including bus usage desired information to saidany other electronic device via said bus; transmitting means fortransmitting bus usage information answering said request for bus usagefrom said any other electronic device via said bus in response to thetransmitted request for said bus usage from said any other electronicdevice via said bus; and receiving means for receiving said bus usageinformation from said any other electronic device via said bus, whereinsaid bus usage desired information and said bus usage informationincludes at least a bus transferring capacity, a starting time of bususage, and a finishing time of bus usage information.
 3. In a systemincluding a plurality of electronic devices connected to each other by abus, wherein each electronic device is capable of transmitting orreceiving information to and from any other electronic device via saidbus, each electronic device comprising: transmitting means fortransmitting a request for bus usage including bus usage desiredinformation to said any other electronic device via said bus;transmitting means for transmitting bus usage information answering saidrequest for bus usage from said any other electronic device via said busin response to the transmitted request for said bus usage from said anyother electronic device via said bus; receiving means for receiving saidbus usage information from said any other electronic device via saidbus; and judging means for judging a possibility of bus usage for adesired bus usage time based upon said bus usage information receivedfrom said any other electronic device and said bus usage desiredinformation, wherein said bus usage desired information and said bususage information includes at least a bus transferring capacity, astarting time of bus usage, and a finishing time of bus usageinformation.
 4. In a system including a plurality of electronic devicesconnected to each other by a bus, wherein each electronic device iscapable of transmitting or receiving information to and from any otherelectronic device via said bus, each electronic device comprising:transmitting means for transmitting a request for bus usage includingbus usage desired information to said any other electronic device viasaid bus; transmitting means for transmitting bus usage informationanswering said request for bus usage from said any other electronicdevice via said bus in response to the transmitted request for said bususage from said any other electronic device via said bus; and receivingmeans for receiving said bus usage information from said any otherelectronic device via said bus, wherein said judging means judges saidpossibility of bus usage based on bus usage desired information inputtedfrom an input means and said bus usage information received from saidany other electronic device, and wherein said bus usage desiredinformation and said bus usage information includes at least a bustransferring capacity, a starting time of bus usage, and a finishingtime of bus usage information.
 5. In a system including a plurality ofelectronic devices connected to each other by a bus, wherein eachelectronic device is capable of transmitting or receiving information toand from any other electronic device via said bus, an electronic devicebus usage method performed in each electronic device, comprising thesteps of: transmitting inquiring information including bus usage desiredinformation to a second electronic device via said bus from a firstelectronic device; receiving bus usage information transmitted from saidsecond electronic device via said bus; and judging a possibility of saidbus usage based upon said received bus usage information and said bususage desired information, wherein said bus usage desired informationand said bus usage information includes at least bus transferringcapacity, starting time of bus usage, and finishing time of bus usageinformation.
 6. In a system including a plurality of electronic devicesconnected to each other by a bus, wherein each electronic device iscapable of transmitting or receiving information to and from any otherelectronic device via said bus, an electronic device bus usage methodperformed in each electronic device, comprising the steps of:transmitting inquiring information including bus usage desiredinformation to a second electronic device via said bus from a firstelectronic device; receiving bus usage information transmitted from saidsecond electronic device via said bus; and judging a possibility of saidbus usage based upon said received bus usage information and said bususage desired information, wherein said bus usage information is onlyextracted when said bus usage information stored in said secondelectronic device corresponds to said bus usage desired information, andwherein said bus usage desired information and said bus usageinformation includes at least bus transferring capacity, starting timeof bus usage, and finishing time of bus usage information.
 7. Anelectronic device for use in a system including a plurality ofelectronic devices connected to each other by a bus, wherein eachelectronic device is capable of transmitting or receiving information toand from any other electronic device via said bus, said electronicdevice comprising: a communicating unit for transmitting or receivinginformation to or from a second electronic device via a bus; aprocessing unit for producing information to be transmitted via thecommunicating unit and for processing information to be received via thecommunicating unit; and a storing unit for storing therein informationused in a processing operation at the processing unit, wherein theprocessing unit creates a bus usage information transmitting requestincluding bus usage desired information that requests the secondelectronic device connected thereto via the bus to transmit bus usageinformation including a start time, a finish time and a requiredbandwidth of the bus usage, and transmits the bus usageinformation-transmitting request through the communicating unit,receives bus usage information relating to the bus usageinformation-transmitting request, judges whether the bus relating tosaid bus usage desired information can be used by comparing the bususage information received with said bus usage desired informationincluding a desired bus usage start time and a desired bus usage finishtime of the own electronic device, and if the bus relating to said bususage desired information can be used, stores the bus usage informationbased on said bus usage desired information in the storing unit.
 8. Anelectronic device according to claim 7, wherein when the request oftransmitting the bus usage information is made, the request oftransmission is made at the second electronic device with the desiredbus usage start time and the desired bus usage finish time of the ownelectronic device being attached thereto.
 9. An electronic device foruse in a system including a plurality of electronic devices connected toeach other by a bus, wherein each electronic device is capable oftransmitting or receiving information to and from any other electronicdevice via said bus, said electronic device comprising: a communicatingunit for transmitting or receiving information to or from a secondelectronic device via a bus; a processing unit for producing informationto be transmitted via the communicating unit and for processinginformation to be received via the communicating unit; and a storingunit for storing therein information used in processing operation at theprocessing unit; wherein, when the communicating unit receives a bususage information transmitting request including bus usage desiredinformation via the bus, the processing unit transmits the bus usageinformation including the start time, the finish time and the desiredbandwidth of the bus usage stored in the storing unit, via thetransmitting unit.
 10. An electronic device according to claim 9,wherein when the transmitting unit receives the desired bus usage starttime and the desired bus usage finish time, together with the bus usageinformation transmitting request, the bus usage information including atime period overlapping a time period indicated by the desired bus usagestart time and the desired bus usage finish time, of the bus usageinformation stored in the storing means is extracted and transmitted viathe communicating unit.
 11. An electronic device for use in a systemincluding a plurality of electronic devices connected to each other by abus, wherein each electronic device is capable of transmitting orreceiving information to and from any other electronic device via saidbus, said electronic device, comprising: means for transmitting bususage desired information that requests bus usage information includinga bus usage start time, a bus usage finish time and a desired bandwidthof the electronic device to the second electronic device; and means forreceiving bus usage information transmitted from the second electronicdevice based on said bus usage desired information that requests the bususage information transmitted to the second electronic devices via thebus, wherein the bus usage information received is compared with the bususage desired information including the desired bus usage start time andthe desired bus usage finish time of the own electronic device tothereby judge whether or not the bus can be used.
 12. An electronicdevice system in which at least two electronic devices are connected toeach other on a bus so as to transmit or receive data to or from eachother, comprising: a first electronic device; and a second electronicdevice, wherein the first electronic device requests the secondelectronic device to transmit bus usage information including a bususage start time, a bus usage finish time and a desired bandwidth,wherein the second electronic device that has received the request oftransmitting the bus usage information transmits bus usage informationstored therein to the first electronic device, wherein the firstelectronic device that has received the bus usage information comparesthe bus usage information received with bus usage desired informationincluding a desired bus usage start time and a desired bus usage finishlime of the own electronic device to thereby judge whether or not thebus relating to the bus usage desired information can be used, andwherein if the bus relating to the bus usage desired information can beused, the first electronic device stores and holds the bus usageinformation based on the bus usage desired information.
 13. Anelectronic device system in which at least two electronic devices areconnected to each other on a bus so as to transmit or receive data to orfrom each other, comprising: a first electronic device; and a secondelectronic device, wherein the first electronic device indicates to asecond electronic device a desired bus usage start time and the desiredbus usage finish time of the own bus usage, and makes a request oftransmitting bus usage information including a start time, a finish timeand a desired bandwidth of bus usage to the second electronic device,wherein the electronic device that has received the request oftransmitting the bus usage information extracts bus usage informationincluding a time period overlapping a time period indicated by thedesired bus usage start time and the desired bus usage finish time, ofthe bus usage information stored therein, and transmits the bus usageinformation to the first electronic device, wherein the first electronicdevice that has received the bus usage information compares the bususage information received with a bus usage desired informationincluding a desired bus usage start time and the desired bus usagefinish time of the own electronic device to thereby judge whether or notthe bus relating to the bus usage desired information can be used, andwherein if the bus relating to the bus usage desired information can beused, the first electronic device stores and holds the bus usageinformation based on the bus usage desired information.